In the semiconductor fabrication industry, marks or numbers on surfaces of silicon wafers may be provided for identification purpose. These identification marks or numbers are used to track different lots of silicon wafers that are manufactured. The tracking marks or numbers can be used, for example, to call back a suspected defective lot where there may be a quality issue or discrepancy. Additionally, the identification marks or numbers can be used to indicate different characteristics of the silicon wafers.
One approach for providing identification marks or numbers on a silicon wafer uses a laser scribing technique to directly cut the identification marks or numbers into the silicon layer. In a typical semiconductor fabrication process where a silicon wafer is coated with an insulating layer, the identification technique includes the step of laser scribing through the insulating layer into the silicon. The insulating layer frequently is silicon nitride deposited onto silicon dioxide, or any other non-oxidizing insulating materials.
FIG. 1 is a cross-sectional view of a silicon wafer 10 having a laser scribe mark 12. The product of direct laser scribing, silicon wafer 10, is shown. The silicon wafer 10 comprises the laser scribe mark 12 which has a first side wall 14, a second side wall 16 and a bottom wall 18 which defines an etched area 20. The etched area 20 occupies a volume that is defined by the width of the bottom wall 18 times the height of either the first side wall 14 or the second side wall 16 times the length (not shown) of the mark made in the silicon wafer 10. The volume defined by the etched area 20 also represents an amount of silicon that is removed from the silicon wafer 10. The silicon is removed by a laser scribe machine (not shown) or other cutting or burning tools. The removal by the laser scribe of a predetermined amount of silicon material creates a "silicon slag" (i.e., silicon particles or dust). The silicon slag generated is excess material that can contaminate the wafer and its surrounding environment and thus adversely affect the fabrication process, in the later steps when the slag is washed out of the mark in a wet chemical etch process.
It is desirable to reduce or eliminate the amount of silicon slag generated. Silicon slag has similar electrical and other physical characteristics as the underlying silicon wafer 10. Additionally, the etched area 20 can create stresses which can cause defects in the silicon wafer 10. The defects in turn reduce the yield of the fabrication process. It is thus advantageous to reduce stresses created in the silicon wafer near the etched area 20.